1. Field of the Invention
The present invention relates to a method of fabricating an optical element, and more particularly to a method of fabricating a periodic domain inversion structure.
2. Description of Related Art
In 1962, Bleombergen et al. proposed a light wavelength conversion technique, wherein a light wavelength conversion element is used to convert a fundamental wave into a second harmonic wave. The light wavelength conversion element is a periodic domain inversion structure having several domains, wherein the domains comprise a spontaneous polarized ferroelectric material, one half of the domains have a polarized direction being opposite to that of the other half of domains, and the two kinds of domains are alternately arranged into a periodic distribution. The application field for such light wavelength conversion element includes a wavelength division multiplexing (WDM) for an optical communication network and red, green and blue laser beams used in displays, and so on.
The formation of domain inversion structure is used a high voltage to drive the movement of the lattice. So the domain must be link properly to electrode with high voltage and can be fabricated through the steps shown in FIGS. 1A-1C. FIGS. 1A-1C are schematic views of a conventional fabrication method of a periodic domain inversion structure. First, referring to FIG. 1A, a nonlinear optical ferroelectric material substrate 100 is provided and coated a photoresist layer 102. A photo mask 103 is disposed over the photoresist layer 102. Then, Referring to FIG. 1B, the periodic photoresist pattern 102a is formed through an optical lithography process. Next, referring to FIG. 1C, a periodic pulse voltage Vp is applied to the substrate 100 with the exposed parts of the substrate such that the electric field formed by the pulse voltage Vp controls the spontaneous polarization direction of the substrate 100, thus, the substrate 100 is divided into domains 100a and domains 100b, wherein the domains 100a have a polarization direction of P+, the domains 100b have a polarization direction of P−, and the polarization directions of P+ and P− are opposite to each other. Thus, the substrate 100 becomes a periodic domain inversion structure.
The periodic photoresist pattern can be fabricated through optical lithography process with mask aligner, however such equipment is very difficult to fabricate the short periodic photoresist patterns. And it must be applied to exposing apparatus such as a stepper or a scanner, thus, the manufacturing cost is relatively high. In addition, as the Internet and the electronic science and technology prevail, the demand for simplicity and low cost periodic domain inversion structures has gradually increased, and is highly desirable for manufacturers in this field.